This invention is concerned with sewing machines; more particularly, it is concerned with a differential feed system for use in an overedge sewing machine and having a safety device to prevent the setting of a differential feed, which would cause interference of parts of the sewing machine.
In a differential feed system, a rear or main feed dog is provided for feeding the work material through the sewing machine, and a front feed dog is utilized to gather the work material as it passes beneath the sewing needle or to stretch the work material, depending upon the work material utilized and the intentions of the sewing machine operator. It is usual in a differential feed system to provide for separate stitch length regulators for the front feed dog and the rear feed dog. Where the front feed dog movement exceeds that of the rear feed dog, material gathering takes place which may have an ornamental effect, such as shirred sleeves of a garment, for example. If the fabric is closely woven and soft in nature, it will require "stretch" in which the rear feed dog feeds faster than the forward feed dog, so that the article will maintain a natural appearance. Generally, in order to obtain the "gather" or the "stretch", the range of motion of the front feed dog is regulated. Thus, a wide range of motions are possible for the front feed dog, including motions which might interfere with other parts of the sewing machine, or the frame thereof.
What is required is a differential feed system having the independent selectability of the feed for the rear feed dog and for the forward feed dog and the capability to avoid the possible interference of parts.